Add option in alt+enter (hint menu) for move string as class constant.

Scenario:
1)
class A
{
... 
  /** @var SimpleXMLElement */
  $xml->addChild('xmltag'); // alt+enter here
...
} 

2)
class A
{
const TAG_A = 'xmltag';
....
}


The main usecase for this feature is:
While coding the programmer can use some non-defined strings. So he needs to create them or come back and create them later. With this feature he/she can create new constants on the fly.

(I do expect some simple dialog for constant name)
Bonus behaviour:
- create constant in parent class
- create constant in class, from which the programmer is already using contants